High Wall Mining is a term applied to various approaches to removing coal and other desired materials in seams or veins under an overburden too deep to justify strip mining. The term is applicable where the appropriate machinery can be present in a cut or bench and extend a mechanism, including a conveyor and terminating with a cutter head or drum, generally horizontally into the vein or seam under a high overburden. The process normally leaves extended pillars between the generally horizontal extended holes,
Such parallel horizontal holes and extended pillars are depicted by Todd in his disclosure in U.S. Pat. No. 4,014,574 of a "Mining Machine Having Rectangular Thrust Transmitting Conveyor Column." Todd employs a "non-thrust-transmitting" screw conveyor to move the cut material out of the hole.
An early patent by Osgood, U.S. Pat. No. 2,415,217, describes the powering of an initial. conveyor belt by a motor mounted on the cutter unit, which also provides forward thrust (col. 3 lines 62 et seq; col 6, lines 50 et seq).
Conveyor belt frame modules are advanced with the cutter head by Brais in U.S. Pat. No. 4,890,720, permitting a single long conveyor belt to be used over several modular units. Such a system requires an independent means for moving the frame modules over the belt to the advancing head of the train, and is not practical in high wall mining.
In U.S. Pat. No. 5,112,111, Addington et al describe interconnected conveyor units for moving the cut material along the cutting extension for recovery. The conveyor units are individually powered, i.e. each has its own motor and gear box for moving the conveyor belt. See also Addington et al U.S. Pat. Nos. 5,261,729, 5,232,269, and 5,364,171, and the individually powered conveyor units of Bargel et al in U.S. Pat. No. 3,992,060. A power system such as Addington's requires manually connecting the motors in series as the conveyor units are placed in tandem, which means that power connections must be made at the unit al.ready in place as well as on the new unit; each of the heavy, bulky explosion-proof electric cable connections must be separately secured manually and comply with safety regulations. Each time a new segment is added to the conveyor system, delays occur clue to the time required for the manual connections as is common in conventional systems.